To prevent unauthorized access to a vehicle, modern access systems or rather access arrangements in vehicles use electronic security systems in which data is communicated between a first communication device of the user (a portable user identification device or identifier, such as a key or key fob) and a second communication device of the vehicle in order to authorize a user. If authorization is successful, a locking system of the vehicle is instructed to unlock a particular vehicle door or all the vehicle doors.
With so-called active access systems, authentication is initiated by a user pressing a particular vehicle unlocking button on his identifier, which then transmits an unlocking signal to the vehicle from a distance. With passive access systems or methods, an authentication code is initiated e.g. by contact with integrated proximity or locking sensors in a vehicle door handle; in response to this contact, the vehicle transmits a code request signal to the identifier which finally, on receiving the request signal, sends back a response signal with the corresponding authentication code to the vehicle. In the vehicle, checking of the received code can then take place and, in the event of a positive i.e. successful check, as already mentioned above, the vehicle or more specifically the vehicle doors are unlocked. It is also possible for an identifier, e.g. in the form of an electronic key, to be designed both for an active and a passives access method.
In the case of a vehicle starter system, in a similar manner to a passive access system, code information can be transmitted from the identification device to the vehicle by means of a dialog consisting of a request signal from the vehicle and a corresponding response signal from the identification device in order to enable, for example, an immobilizer to be deactivated or a vehicle propulsion system to be started.
In addition to the actual “short-range” application of obtaining access to a vehicle located in the immediate vicinity or of starting its propulsion system, longer-range applications are planned in which user identification devices such as vehicle keys can also communicate with the vehicle over greater distances. Modern access or starter systems are also designed such that they normally have a plurality of user identification devices or keys, for gaining access to the vehicle or starting the vehicle propulsion system. It may now happen that, for example, two people have been traveling in a vehicle, both of whom are carrying with them a key associated with the vehicle's access system. If the vehicle is parked, and the two people get out of the vehicle, and e.g. one of the people mislays the key inside the vehicle or outside in close proximity to the vehicle, this mislaid key represents a security risk, as it can be used by unauthorized persons to gain access to the vehicle and/or start the propulsion system. Particularly if the key slips down into poorly visible pockets in a side door of the vehicle, for example, or if it is lost outside the vehicle under a pile of mud or leaves, this makes it very difficult to notice that the user identification device has been mislaid and to subsequently locate it. The key is then mainly regarded as lost.